An adult human resting heart rate is normally 60 to 100 beats per minute, while shrews clock in at “over 1,000 beats per minute—that’s over 16 times a second,” Mark Oyama, cardiology professor at the University of Pennsylvania School of Veterinary Medicine, says via email.

The average weight of a dog heart is about 0.7 to 0.8 percent of their body weight, whereas in cats it's about 0.35 percent.

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A sea star, alas, does not have a heart.

Photograph by Paul Nicklen, National Geographic

Lopsided Heart

Giraffe hearts aren’t unusually large for their size, Rachel Brand, an independent behavioral ecologist in Namibia, says via email—but you could say they’re a little one-sided.

A giraffe heart’s left wall ventricle can be up to 3.24 inches (about 8 centimeters) thick, compared with its right ventricle wall, which is about 0.6 inch (1.5 centimeters) thick. Thickness indicates muscle power.

Cephalopods like squid and octopus usually have three hearts: One systemic heart that pumps blood through the rest of the body after the hearts have pumped it to the gills, where oxygen is taken up.

Epic Octopus Fight Caught on Video

New footage shot off southeastern Australia suggests that Sydney octopuses broadcast their intentions to each other, either to avoid or to escalate conflict.

And then some animals have no heart at all.

Sea stars, aka starfish, and other echinoderms “do not have a ‘heart’ or anything analogous to it,” Chris Mah, a marine invertebrate zoologist at the Smithsonian National Museum of Natural History in Washington, D.C., says via email.

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